Diarrheal disease, particularly in children residing in developing countries, is still a major cause of illness and death. Estimates for the late 1970s and early 1980s [1] suggested that in Asia, Africa, and Latin America alone more than 5 billion episodes of diarrheal illness and 5 to 10 million diarrhea-associated deaths occurred annually. More recent estimates [2] from the World Health Organization provide additional perspective on the worldwide problem of diarrheal illness in children. The World Health Organization estimated that in 1991, 4.3 million deaths occurred in children from acute respiratory infections, 3.5 million from diarrheal diseases, approximately 1 million from malaria, and 0.88 million from measles. Data from more than 100 geographically based surveys clearly show that cryptosporidia are one of the major enteropathogens causing diarrheal illness worldwide and that this enteropathogen contributes substantially to illness and death among children, especially malnourished children in developing countries [3].